This article examines the objectives and methods of fireproofing works for buildings and structures of nuclear power plants. It analyzes the requirements of NP-509, NP-511, and other regulatory documents for the fire resistance of building structures, limitation of fire spread, and use of non-combustible materials. It describes methods for improving the fire resistance of steel and concrete structures, replacing fire-hazardous materials, installing fire barriers, and applying fireproof coatings. Recommendations are provided for an integrated approach to fire protection at facilities using nuclear energy (FUNE).
Ensuring fire safety at nuclear power facilities is one of the priority areas, because fire can lead to failure of safety systems, loss of reactor control, and radiological consequences. Unlike general industrial buildings, NPPs are subject to special requirements: not only fire-resistance ratings of structures (R, REI), but also limitations on flame spread, smoke generation, toxicity of combustion products, and resistance of fireproofing to decontamination and ionizing radiation.
Fireproofing works at facilities using nuclear energy include treatment of steel and reinforced-concrete structures with fireproofing compounds, replacement of combustible materials with non-combustible materials, installation of fire partitions and doors, sealing of cable penetrations, and modernization of existing buildings to improve their fire safety.
Regulatory Framework for Fireproofing at NPPs
The main documents governing fireproofing requirements at facilities using nuclear energy are:
• NP-509-21, Fire Safety Rules for Nuclear Power Plants, establishes the mandatory use of non-combustible and flame-retardant materials and the required fire-resistance limits for structures depending on the safety class of the room.
• NP-511-21, Requirements for Fire Protection Systems of Nuclear Power Plants, regulates passive and active fire protection systems, including fireproofing of building structures.
• Federal Law No. 123-FZ, Technical Regulations on Fire Safety Requirements, applies to the classification of construction materials by combustibility (G1-G4, NG) and structural fire hazard.
• STO 95 12009-2017 (rules for concurrent works) also contains sections on fire safety during construction and installation works.
Classification of Construction Materials by Combustibility
For NPP facilities, NG-class (non-combustible) or G1-class (low-combustibility) materials with low smoke generation and no halogen release are preferred. Replacement of fire-hazardous materials (wood, foam plastic, unmodified bitumen compounds) with non-combustible or fire-protected materials is mandatory during reconstruction and overhaul.
Ensuring fire safety at nuclear power facilities is one of the priority areas, because fire can lead to failure of safety systems, loss of reactor control, and radiological consequences. Unlike general industrial buildings, NPPs are subject to special requirements: not only fire-resistance ratings of structures (R, REI), but also limitations on flame spread, smoke generation, toxicity of combustion products, and resistance of fireproofing to decontamination and ionizing radiation.
Fireproofing works at facilities using nuclear energy include treatment of steel and reinforced-concrete structures with fireproofing compounds, replacement of combustible materials with non-combustible materials, installation of fire partitions and doors, sealing of cable penetrations, and modernization of existing buildings to improve their fire safety.
Regulatory Framework for Fireproofing at NPPs
The main documents governing fireproofing requirements at facilities using nuclear energy are:
• NP-509-21, Fire Safety Rules for Nuclear Power Plants, establishes the mandatory use of non-combustible and flame-retardant materials and the required fire-resistance limits for structures depending on the safety class of the room.
• NP-511-21, Requirements for Fire Protection Systems of Nuclear Power Plants, regulates passive and active fire protection systems, including fireproofing of building structures.
• Federal Law No. 123-FZ, Technical Regulations on Fire Safety Requirements, applies to the classification of construction materials by combustibility (G1-G4, NG) and structural fire hazard.
• STO 95 12009-2017 (rules for concurrent works) also contains sections on fire safety during construction and installation works.
Classification of Construction Materials by Combustibility
For NPP facilities, NG-class (non-combustible) or G1-class (low-combustibility) materials with low smoke generation and no halogen release are preferred. Replacement of fire-hazardous materials (wood, foam plastic, unmodified bitumen compounds) with non-combustible or fire-protected materials is mandatory during reconstruction and overhaul.
Methods of Fireproofing Works at NPPs
1. Fireproofing of Steel Structures
Steel columns, beams, trusses, and bracing in NPP buildings rapidly lose load-bearing capacity during a fire (at 500-600°C the yield strength of steel is reduced by half). The following are used to increase the fire-resistance limit to the required R90, R120, or R180:
• Thin-layer intumescent coatings (which expand when heated to 150-250°C) with a dry-film thickness of 0.5-3 mm, providing R60-R150. These compounds are based on polyurethane, epoxy resin, or acrylic. Radiation-resistance verification is required for zones with doses above 10^5 Gy.
• Thick-layer cement and perlite plasters (15-40 mm thick) provide R90-R240, are non-combustible and radiation-resistant, but are heavy and increase the section thickness.
• Fireproof boards and linings (vermiculite, gypsum-fiber boards, basalt mats) are used for hard-to-reach areas and where the appearance must be preserved.
• Hybrid liquid-glass coatings combine the properties of inorganic and organic systems and have pendulum moisture release, which helps prevent hydrogen explosion.
Before applying the coating, steel structures are cleaned to Sa 2.5 (abrasive blasting) and primed with a compatible primer. Thickness is controlled with a magnetic thickness gauge, and adhesion is checked by cross-cut or pull-off testing.
2. Fireproofing of Reinforced-Concrete Structures
The fire resistance of reinforced concrete depends on the thickness of the protective concrete cover over the reinforcement. If the cover is insufficient (less than 20 mm), concrete cracks and spalls when heated, and the reinforcement is exposed and loses strength. Fireproofing works include:
• Increasing the protective cover (shotcreting, plastering with vermiculite-cement mortar).
• Fireproof paints for concrete (intumescent compounds, 0.5-2 mm thick).
• Replacement of damaged concrete with heat-resistant concrete (aluminate cement) during repair.
3. Replacement of Fire-Hazardous Materials and Structures
When reconstructing existing buildings built before modern standards were introduced, the following must be replaced:
• Wooden rafters and floors with steel or reinforced-concrete structures with fireproofing.
• Expanded-polystyrene insulation (G3-G4) with NG-class basalt wool.
• Unprotected cable routes with NG-LS (low-smoke) coated cables and firestop penetrations.
• Fire-hazardous wall and ceiling finishes (PVC panels, wood-fiber boards) with non-combustible or G1 materials.
Dismantling of old materials and installation of new ones are carried out under a Work Execution Plan agreed with the fire-safety department.
4. Installation of Fire Barriers
In addition to fireproofing of load-bearing structures, fire barriers are installed:
• Type 1-2 fire walls and partitions (REI 150, REI 120) made of brick or blocks and filled with non-combustible insulation.
• Fire doors and hatches (EI 60, EI 90) with automatic closers and seals.
• Fire-protected penetrations for pipes, cables, and air ducts through walls and floors (fire-resistant collars, embeds with mineral wool, sealants).
Quality Control of Fireproofing Works
Acceptance of fireproof coatings and structures at NPPs is carried out according to the following parameters:
• Coating thickness (not less than the design value; measurements at 5 points per 1 m²).
• Continuity (absence of gaps, cracks, and delamination, checked visually and by tapping).
• Adhesion to the substrate (cross-cut or pull-off method, not less than 1.0 MPa for epoxy compounds).
• Fire tests (for new materials, a report from an accredited laboratory; for serially used materials, a fire-safety certificate and product passport).
• Radiation resistance (when used in a controlled access zone, an irradiation-dose test report).
All results are documented in concealed-work inspection certificates (for coatings later covered by finishing layers) or acceptance-control certificates.
Conclusions and Recommendations
Integrated fire protection of NPP facilities must include not only treatment of steel structures but also replacement of combustible materials, installation of barriers, and sealing of penetrations. It is recommended to:
1. At the design stage of new construction, specify non-combustible materials (NG or G1 class) and structural solutions with the required fire-resistance limit under NP-509.
2. For existing buildings, conduct an audit of fire-hazardous materials and develop a replacement program with phased fireproofing of the most important load-bearing structures.
3. For safety class 1-2 steel structures, use fireproofing with a service life of at least 50 years (inorganic linings or hybrid liquid-glass coatings).
4. Ensure quality control at all stages: incoming inspection of materials, operational control of thickness and adhesion, and acceptance testing.
5. For strict-regime zones, additionally verify the decontaminability and radiation resistance of fireproofing compounds.
To obtain a commercial proposal for fireproofing works (application of intumescent coatings, installation of fire barriers, replacement of fire-hazardous materials with non-combustible ones, and sealing of cable penetrations) at your facility, send a technical specification indicating the type of structures, required fire-resistance limits (R, REI), room safety class, and operating conditions to the commercial department of TechAtomStroy LLC via the feedback form on the website. A cost estimate, work schedule, and optimal fireproofing systems selected with NP-509 requirements in mind will be prepared.
*This material was prepared on the basis of NP-509-21, NP-511-21, Federal Law No. 123-FZ, and GOST R 53293-2009.*
1. Fireproofing of Steel Structures
Steel columns, beams, trusses, and bracing in NPP buildings rapidly lose load-bearing capacity during a fire (at 500-600°C the yield strength of steel is reduced by half). The following are used to increase the fire-resistance limit to the required R90, R120, or R180:
• Thin-layer intumescent coatings (which expand when heated to 150-250°C) with a dry-film thickness of 0.5-3 mm, providing R60-R150. These compounds are based on polyurethane, epoxy resin, or acrylic. Radiation-resistance verification is required for zones with doses above 10^5 Gy.
• Thick-layer cement and perlite plasters (15-40 mm thick) provide R90-R240, are non-combustible and radiation-resistant, but are heavy and increase the section thickness.
• Fireproof boards and linings (vermiculite, gypsum-fiber boards, basalt mats) are used for hard-to-reach areas and where the appearance must be preserved.
• Hybrid liquid-glass coatings combine the properties of inorganic and organic systems and have pendulum moisture release, which helps prevent hydrogen explosion.
Before applying the coating, steel structures are cleaned to Sa 2.5 (abrasive blasting) and primed with a compatible primer. Thickness is controlled with a magnetic thickness gauge, and adhesion is checked by cross-cut or pull-off testing.
2. Fireproofing of Reinforced-Concrete Structures
The fire resistance of reinforced concrete depends on the thickness of the protective concrete cover over the reinforcement. If the cover is insufficient (less than 20 mm), concrete cracks and spalls when heated, and the reinforcement is exposed and loses strength. Fireproofing works include:
• Increasing the protective cover (shotcreting, plastering with vermiculite-cement mortar).
• Fireproof paints for concrete (intumescent compounds, 0.5-2 mm thick).
• Replacement of damaged concrete with heat-resistant concrete (aluminate cement) during repair.
3. Replacement of Fire-Hazardous Materials and Structures
When reconstructing existing buildings built before modern standards were introduced, the following must be replaced:
• Wooden rafters and floors with steel or reinforced-concrete structures with fireproofing.
• Expanded-polystyrene insulation (G3-G4) with NG-class basalt wool.
• Unprotected cable routes with NG-LS (low-smoke) coated cables and firestop penetrations.
• Fire-hazardous wall and ceiling finishes (PVC panels, wood-fiber boards) with non-combustible or G1 materials.
Dismantling of old materials and installation of new ones are carried out under a Work Execution Plan agreed with the fire-safety department.
4. Installation of Fire Barriers
In addition to fireproofing of load-bearing structures, fire barriers are installed:
• Type 1-2 fire walls and partitions (REI 150, REI 120) made of brick or blocks and filled with non-combustible insulation.
• Fire doors and hatches (EI 60, EI 90) with automatic closers and seals.
• Fire-protected penetrations for pipes, cables, and air ducts through walls and floors (fire-resistant collars, embeds with mineral wool, sealants).
Quality Control of Fireproofing Works
Acceptance of fireproof coatings and structures at NPPs is carried out according to the following parameters:
• Coating thickness (not less than the design value; measurements at 5 points per 1 m²).
• Continuity (absence of gaps, cracks, and delamination, checked visually and by tapping).
• Adhesion to the substrate (cross-cut or pull-off method, not less than 1.0 MPa for epoxy compounds).
• Fire tests (for new materials, a report from an accredited laboratory; for serially used materials, a fire-safety certificate and product passport).
• Radiation resistance (when used in a controlled access zone, an irradiation-dose test report).
All results are documented in concealed-work inspection certificates (for coatings later covered by finishing layers) or acceptance-control certificates.
Conclusions and Recommendations
Integrated fire protection of NPP facilities must include not only treatment of steel structures but also replacement of combustible materials, installation of barriers, and sealing of penetrations. It is recommended to:
1. At the design stage of new construction, specify non-combustible materials (NG or G1 class) and structural solutions with the required fire-resistance limit under NP-509.
2. For existing buildings, conduct an audit of fire-hazardous materials and develop a replacement program with phased fireproofing of the most important load-bearing structures.
3. For safety class 1-2 steel structures, use fireproofing with a service life of at least 50 years (inorganic linings or hybrid liquid-glass coatings).
4. Ensure quality control at all stages: incoming inspection of materials, operational control of thickness and adhesion, and acceptance testing.
5. For strict-regime zones, additionally verify the decontaminability and radiation resistance of fireproofing compounds.
To obtain a commercial proposal for fireproofing works (application of intumescent coatings, installation of fire barriers, replacement of fire-hazardous materials with non-combustible ones, and sealing of cable penetrations) at your facility, send a technical specification indicating the type of structures, required fire-resistance limits (R, REI), room safety class, and operating conditions to the commercial department of TechAtomStroy LLC via the feedback form on the website. A cost estimate, work schedule, and optimal fireproofing systems selected with NP-509 requirements in mind will be prepared.
*This material was prepared on the basis of NP-509-21, NP-511-21, Federal Law No. 123-FZ, and GOST R 53293-2009.*